BABY HUG is a randomized, double-blind, placebo-controlled trial to determine if hydroxyurea can prevent the onset of chronic end organ damage in young children with sickle cell anemia. BABY HUG follows the successful completion of two other sickle cell disease trials, the Multicenter Study of Hydroxyurea in Sickle Cell Anemia (MSH) and the Pediatric Hydroxyurea (PED HUG) Trial. Approximately 200 children, ages six months to 24 months, with sickle cell disease will be recruited to receive either hydroxyurea or placebo. The children will be screened at trial start-up for signs of abnormal brain, renal, pulmonary, and splenic function, and for developmental milestones. They will then be randomly assigned to receive hydroxyurea or a placebo and followed with yearly studies of chronic end organ damage of the major organ systems.